The invention relates to an electric circuit-breaker with self blow-out by rotation of the arc under the effect of a magnetic field generated by the current to be cut. The circuit breaker includes:
a sealed chamber filled with a gas of high dielectric strength, PA0 a stationary contact assembly, mounted freely inside the sealed chamber, PA0 an annular electrode pertaining to said stationary contact assembly and forming an annular track for the rotation of the arc under the effect of a magnetic field generated by a tubular coil fitted coaxially at the rear side of the annular electrode, PA0 a ferromagnetic core extending coaxially inside the tubular coil and presenting a terminal face adjacent to said annular electrode, PA0 and a channel contrived in said stationary contact assembly and passing through the tubular coil and the annular electrode.
Known circuit-breakers require only a very small amount of opening energy, due to the fact that the arc blow-out magnetic field is derivated from the current to be cut. The core is made up of a tubular metal element of ferromagnetic material which delimits the passage for the gas. This passage has a circular cross-section and contains a device which absorbs the decomposition residues of the blow-out gas. The device is fitted between two metal grids which cleanse and cool the blow-out gases. However, the presence of this device inside the channel holds up the normal flow of the outgoing gas and can lead to the formation of an ionized gas lock in the arc zone. The coil is surrounded coaxially by a ferromagnetic tubular yoke extending as a deflector contrived around the arc expansion zone. This deflector protects the chamber from the effects of the arc, but holds up the flow of gas around the stationary contact assembly. As a consequence, the cutting capacity of such a circuit breaker is limited.
The object of this invention is to overcome this difficulty and to make possible the manufacturing of an effective rotating arc circuit breaker.
According to the invention, the expansion zone of the arc at the front side of the stationary contact assembly communicates freely with the opposite rear zone, both through and around said assembly, the first inside trajectory of the gas passing through said channel, and the second trajectory passing outside between said stationary contact assembly and the inner wall of the chamber.
Tests have proved the efficiency of this device, which can be explained by an easier evacuation of the ionized gas out of the arc zone, namely out of the central zone defined by the rotating arc. It has already been proposed earlier to combine the magnetic blow-out and the pneumatic blow-out of the arc by generating in a rotating arc circuit breaker the blowing-out of the gases out of the arc zone either by a piston system, or by using self-expansion towards a separate expansion compartment. These systems are elaborate and require internal separations in the enclosure and/or of the volumes to be swabbed. Pneumatic blow-out participates to a considerable, sometimes predominant extent in the blowing-out of the arc. The present invention is based on a different conception, in so far that, on the one hand, it increases the magnetic blow-out, i.e. the rotation of the arc, by providing a ferromagnetic core inside the coil, and that, on the other hand, it prevents any formation of a stagnation zone of ionized gases in the central zone defined by the arc. The gases submitted to the effect of the arc can flow out freely on both sides of the arc towards cooler zones of the enclosure, whose total volume is thus used. This gas flow does not carry out any blowing-out of the arc. The core is preferably connected in series with respect to the blow-out coil, in order to maintain the magnetic blow-out in case of a switching of the arc onto the core. The outlet channel may be contrived inside the tubular core or between the internal face of the coil and the external face of a solid core of a smaller diameter, or may combine these two possibilities. The longitudinal profile of the outlet channel has preferably the shape of a jet pipe, with collars to which a contracting inlet is connected upstream, and an expanding outlet downstream, so as to facilitate the flowing out of the gas from the arc zone in the direction of the outlet.
According to a further development of the invention, the blow-out coil is surrounded externally by a yoke intended for strengthening the magnetic field, and the opposite electrode is provided with holes allowing the passage of the gas.
The invention will be described lower in detail as being applied to a circuit breaker with main contacts separated from the arc contacts, such as described in U.S. patent application Ser. No. 319,284, but it may of course be applied to any other type of rotating arc circuit breaker, for instance with main contacts coaxial to the arc contacts, or with separate contacts constituting the rotation tracks of the arc.